Radio locating system



w. H. CAPENV 2,411,520 RADIO LOCATNG SYSTEM y Filed Dec. 22, 1959 Nov. 26, 194e.

3 Sheets-Sheet l ATTOR EY.

Nov. 26, 194e. 2 W. H. CAPEN 2,411,520

RADIO LOCATING SYSTEM y Filed DSC. 22, 1959 5 SheelZS-Sheet 2 FIGB. Wwf/P* ATTO EY.

RADIO LOCATING SYSTEM VHF/449.65'. /71

Effi/VER AIVD @54m/V INV EN TOR. WILL/AM CAPE/V BY y ATTO EY.

Patented Nov. 26, 1946 man UNITED STATES PATENT ortica-j signor to International Standardv` Electric *Gore N. Y., a corporation of poration, New York, Delaware Application December 22, 1939; seriaiffn.` 3ra-51a 9 Claims. l.

My inventi'cm'A relates to distance' and position determining systemsrandmore particularly to systems andQmethods for determining the distance andi position of a` movingl objectV by means of radi'o waves.

Known radiodistancedetermining systems generally depend# upon measurements of the angle athtwoseparate transmitting/points, or upon arrangements' forgivingA an approximate indication of distance by means of signal strength-measurement.

in a'certain type ofdistanceindicatory partieu'larlyusedv forI altimeter purposes, a continuously varied frequency-wave is transmitted to a reflecting* Objectand the distance tothe reecting objectifs-determined* bye means of l a comparison of thei frequencyof the reflected wavewith that of? the wave being transmitted towardsV the ren'e'ctingsurfa'ce'.

This-type" of altix'neter'hasL been found t0 be quite satisfactory as it does not depend uponl measurement offamplitude-of waves nor thecomparisonn of relative amplitudesv thereof, but/"only"y upon a; measurement'E of the frequency difference which depends 1J'.pon`the-'flength of the' transmitl ting path.

Imaccordan'ce with my invention Il provide a" distance determining system-utilizing a frequency varied transmitted'wave andprovide at the point fromwhich the distance is to be determined, Aa transmitterl arrangement responsive to receipt oi the frequency varied waves" for transmitting an*- otlierffrequency varied wave which may be compart-id:L at' the receiver with' reference waveL for indicating the distance.-

Itis a principal object'of my' invention toA pro-l videa radio distance determining means which is` sin'cplel in constructionV` and' positive' in oper'- ation.

ItfisA a still further object of my Yinvention to provideV in" a radio Vdistance determining system meansior simultaneously observingV the direction ofthe distance point, so that the position of the receivingstation' maybe determined.

It is a still further objectof my'i'nven'tion' to prc'ivi'de` an" arrangement wherein frequency mod; ulatd'-wa'ves are transmitted from `a` first point" to a secondv point and are receivedlv attheseeondfpointl and'retransmitted to. the rst point, I

whereby. the distance. between. the two pointsfmay be dtemineal... e

Itis a=still'..irther object offmyl invention! toy providecontrolmeans at .at-.iiked repeater station respnisiyetoV variable .frequency Waves transmit#- 2 ted.' from a moving station for rendering a trans'- mitter at the4 fixed station operative. e u

It is' a' still further object of my invention to provide a further signalling arrangement for in-v dicating the identity of the repeating receiving retransmitting station. Y* M It is a still further object of my invention to provide a lateral guiding beacon which in conjunction with said retransmitting station will pro-` f vide an' indication on the, craft of the location with respect to a` particular point of the earths surface. l Other advantages and objects of. my invention willfbe apparent from the particular descriptin ofia few embodiments thereof,.made in connection with* the.V accompanying drawings inr which v Fig.v 1 is a diagram'illustrating the arrangement infaccordancewithmy invention; l 4 e e Fig. 2 isfal curve used for illustrating the Voperation'of thefreceiving station on the movingl objects;

Fig. Sis a diagram of a retransmitting; station. operating in'accordance with my invention;vr

Fig;` iA is adiagram0 illustrating an arrangement for preventing feedback and consequent singing of the amplifier at the receiving station; Fig, 5 is a modiedretransmitting station in accordance.: with my invention, including anarran'gement" for transmitting staticnidentifying signals;

Fig.k is'lone. form of systemio'r use onY an airplane in the combination of my invention;- Y

Figs '7 is'a'lf'urther modified 4form of distance"v determining receiver arrangement in accordance withimy invention, and t e A4 Figs. 8 and 9 illustrate anA embodiment of my invention wherein 'beacon guidingv is used in-V conjunction with a distance determiningvsystem.

Infaccordance-with my invention I provide, as shown in Fig. 1, onf-af moving craft such as airplaneY l0, an arrangement comprising a transmitter Il, a receiver l2-,`and an indicating meter I3.V Transmitter llv emitsv a wave-which isV continuously cyclically varied betweentwoiixed values.A

vThe transmitter isgenerally operated only at.,

intervalswhen distance indication is desiredand inl the caseotlregular air lines may bev usedonly,y

after permissionis.. given. This transmitted-wave is-received at aiiXed. point on a receiving antenna I4.' Receivingantenna Misfcoupledatova; receiving-and retransmitting device |55, the 'output of which is coupled to atransmitting antenna I6, so that a wave varyingin4 frequency in a manner similar tothe received wave willbe transmitted therefrom.` l

The wave transmitted from antenna I6 is received on craft I by receiver I2. This received wave is then conveyed to indicator I3 and simultaneously a small part of the energy being generated in the transmitter II is also conveyed to indicator I3. Indicator I3 is a frequency meter which indicates the frequency difference between the wave received at I 2 and the Wave' being transmitted from I I. Since the frequency transmitted is continuously varying, the frequency difference is a function of time required for the wave to travel to its respective station and back, plus the time delay of apparatus I4, I5, I6, it is clear that the frequency difference between these waves will indicate the length of the path. The meter I3 may be calibrated directly in distance to provide on the craft a direct indication of its position relative to the receiving and transmitting station.

The function of the indicator may be more clearly understood by reference to Fig. 2. In this figure the solid line curve 2I represents the frequency of the wave transmitted from transmitter Ii with respect to time, and the broken line 22 represents the variation in frequency with respect to time of the wave received at receiver I2. Consequently the distance may be readily obtained from the frequency difference a, b, shown on' the curve, allowing for the constant frequency difference due to the fixed time delay by the repeating station, The calibration ofk the meter can be so made that this is taken care of.

As a typical example of the frequencies involved, assume a normal carrier of 100 mc. and use a frequency variation of 2 me., i. e., the car,- rier varies from minimum of 98 mc. to a maXlmum 102 mc. Assume this variation occurs with a period of 1/5 of second for a complete cycle, i. e., the carrier varies from 98-102 mc. in 1/5 second. Then as radio waves travel 186,000 miles per second a round trip to the ground station and return will be 2/186000 second per mile away from station. Assume miles distance, then time of travel will be /185000 second and carrier difference as received at moving object will be (2O/186000) X4 X 10(i X 5 as carrier varies 4 mc. in 1/5 of a second. This gives 2,150 cycles. For 100 miles the carrier frequency difference will be 21,500 cycles.

On account of the very high speed of such moving objects as airplanes the so-called Doppler effect on the frequency of the carrier as received at the moving object is not negligible. For a plane moving 200 miles per hour directly towards or away from the ground station the Doppler effect will change the 'received frequency by 331/3 cycles per second if the carrier is 100. mc. This is only approximately 11/2% error at a distance of 10 miles and for the conditions used in the example given immediately above and consequently does not introduce too great an error. A suitable arrangement for the frequency variable retransmitter or repeater arrangement is shown in Fig. 3. In this arrangement the receiving antenna is indicated at coupled to an automatic volume controlled receiving amplifier 3l. The output of amplifier 3| is coupled to a network 32 so designed that with constant voltage output the voltage impressed on rectifier 33 is proportional to the received frequency. As is apparent to those skilled in the art, such a network may be readily designed for a predetermined frequency band. as is common in high fidelity receiver circuits. This frequency control means 34 is coupled to an oscillator 35 to vary the frequency of this oscillator in a manner similar to the frequency of the received wave signal.

The output of oscillator 35 is then amplified in anV amplifier 33 and is transmitted from antenna 31. A portion of the received signal is transmitted over line 33, to rectifier 39 and used to'control a trigger tube arrangement 40.

Accordingly, when signals are received on antenna 30, they are rectified at 39 operating tube 43, which is in series between the oscillator output and the amplifier arrangement. Thus the transmitter 35 is rendered effective upon receipt of signals. The frequency modulation of these retransmitted signals is controlled by means of the portion of the signals rectified at 33 by means of control means 34.

In order that the energy transmitted from an tenna 37 does not interfere with that received at 33, that is, is not fed back to the amplifier over antenna 36 to build up;singing oscillations, it is necessary to provide some arrangement whereby such feedback cannot occur. This may be accomplished by,transmitting from antenna 31 a frequency different from that received at 30 and reconverting the energy after receipt on the craft back to the same frequency as that of the craft transmitter. Thus the frequency range of the retransmitted waves may be made to vary correspondingly with the aircraft transmitter but at a frequency range differing therefrom. Feedback may accordingly be prevented by tuning the circuit of receiver 3| to reject the band of frequencies in the range transmitted at 31.

According to this figure an arrangement is provided so that the energy received on antennae 4I, 42 is supplied to an amplifier 43 over branch lines 44, 45. The output circuit of amplifier 43 is coupled to transmitting antenna 46. If the path between the antenna including the coupling lines 44, and 45, and point 4l is made of such length,

that the distance from point 47 to antenna 46 is substantially the same electrically in both directions, except for a 180 phase shift, then energy received on receiving antennae 4I, 42, from any -tenna 46 will neutralize at point 41, so that there v can be no feed into amplifier 43 therefrom. The type of arrangement is explained more in detail in the U. S. Patent 2,134,278, issued October 25, 1938, in the name of Andrew Alford.

be utilized, together with a repeater system such as that shown in Fig. 3, itis also clear that if desired, the amplifier arrangement 43, instead of including the various control elements shown in Fig. 3, may be simply an amplifier which will assume operation upon receipt of signals and retransmit the same signal from antenna 46 as am.. l

plified waves.`

It is often desirable that with any transmitting system, such as the retransmit-.ting arrangement in accordance with this invention, a means may be provided for indicating the identity of the station. Such an arrangement is disclosed in Fig. 5. According to this system the rtransmitting antenna 46 is shown coupled to a switching arrange- It is clear that if instead of reconverting the While the antenna arrangement of Fig. 4 may ment and' a receiving amplier 5|-, to-the receiving antenna; In theposition Shown receiving ampliiier l* tactsof switch 56',- directlyy to thetransmitting amplifier to provide a retransmitting system. Switch- 50i-is controlled by a cam 52 driven from amotor 53 through gears 513-, 55 andf. When cam 52 is rotatedso that the lower portion thereof i's--oppositeswitch 5i), the switch contacts' in the lower' position are closed. Preferably the lower cam portion is shorter than the-raised portion so that the distance indicating transmission is effective for the maior portieri ofthe-time.- Motor-".ilsimultaneously drives-by means of gear 55 arecorddisc Se, which may-'be madeof transparent material and have onits--peripherya` signal indicating the identity of the station. Immediatelybehind dise 60- is providedY a lamp-6| which shines-through the disc onto photocell 62 connected: to a voicefrequency ampliiier 63;. The output of voicefrequency-amplifier S3 is modulated in 64 with high frequency oscillations gen# erated iti-oscillator vE5. In this position modulator lihas? its output connected through the lower contacts ofswitch 50 tothe transmitting amplifier 1li-'and antenna liliy` and sotransmits intermittently distance indicating signals and signals indicating the identity of the station. Preferably the oscillator @5l operates at a frequency such that signals may be received on the regular receiving apparatus, or onthe distance determining receiver. The identifying.Y radio waves may-bereceivedfon theairplane by a-suitablev auxiliary-receivery tuned to the frequencyV of oscillator 65. g

Since the retransmitting station may not be required to operate during alarge portion of the time, it may be-preferaloleto-havey the povverl ampliiier of the transmitter disconnected at times that the signals are not desired.- I accomplish this result according to-onesystenz-i,Y by providing a relay 65 controlled from` the output of receiver amplifier 5i over rectifier-61 -tof close switch 68 connected tothe high tension power supply 69 for the-radio frequency power amplier T9; Whenncl-signals are being received onthe receiving antenna, relayA 66 is deenergized andconnections are opened at 68.- Uponreceipt of signals, however,- the high tension supply B9 is connected to amplifier-61- over contact B8; It is-clearthat other contacts may be provided' under control of relay 66- toenergize motor 53- and the auxiliary apparatus 63', 64, 65ionly during receipt of signals in receiver-5l` to provide further saving in power.

In the-arrangement described above it is evident that should more than one aircraft attempt to obtain distance indication simultaneously, no clear reading -could be obtained-by either since the frequencies received on each aircraft would be-hopelesslyjumbled and no steady-meter readingco'uldbe obtained. However, suchv a condition is' not likely to arise asA usually distancede*- terminations will be madev only at comparatively long intervals. IfV upon attempt to obtain a'distance reading the meter shows that another craft isk also trying to get a reading, the navigator need only continue trials` until a steady indication is obtained.

Should traffic conditions be heavy enough to require it', several repeater stations may be erected at a particular port each responsive to a different' frequency range andthe aircraft circuit may be provided with switching means so that the transmitter may operateselectively at differentfrequency ranges; If one repeater is' then is'conn'ect'ed through upper-conbusy the pilot may try another by changing the frequency range of-this-transmitter.-

In- Fig. 6- is-disclosed--one-form of stationl suitable forusevv on the movable craft lin accordance with my invention. In this system a variable frequency transmitter TI-lsprovided connected to the transmitting antenna 12.- A-rotatable loop antenna 13may-b`e-used for'receiving thesi'gnals, loop 1-3--bei-ngcoupled-toreceiver 'M'. The frequency--variable signals received may thenbe transmitted from receiver Tdt-to indicator-15 and a-l smallpart-of the energy from 1l may loe-trans*- mitted to 15 -to-provide a distance indication-by frequency comparison. Simultaneously loop-13 may be adjusted directively soas to produce ya directive indication in indicator' 16.- By this arrangement bothV the distance and direction of the transmitting staton may be determined; thus enabling an airplane to iind its exact position with reference to the transmitting'station. This may be desirable in scme'cases where a limited landing area isprovided and crafts leavethis area and must return thereto. For example, on an aircraftcarrier it is vital that the'planesbe enabled to return-to the carrier, but itispreferable that they be enabled to fly asia-r as possible so as to make ful-l use ofthe gasoline carried. By use of a system in accordance with my invention, this may be accomplished since the pilot 'of the aircraft will at. all times know' the distance from ther transmitting source and may therefore determine if sufficient gasoline may stay out awhile longer. In additiontothe direction` finding feature 'the aircraft may then head-directly for-the-transmitting station.

In Fig. 7' an` aircraft equipment suitable-fordetermining direction and distance, andin' addition receiving signalsidentifying the relaystation'is illustrated. Inl this arrangement parts similar 'to Fig. 6-l are provided with'th'ev same-reference characters. At the-receiver, in addition to the rotatable loop 73, I have shown an auxiliary'non-directional sensing antenna 18; Of course, iithe direction indication is not desiredv any type of aerial maybe used. In the output of receiver amplifier 'i4 I provide a detector '19.V The output of this detector is connected to an indicating arrangement such as shown by heady phone'- 80 for indicating the ridentity of` the station.A Also; in the output of detector 'i9 is branched the rectier unit 8| which serves to furnish energy for thedirection indicator 15'.

It is sometimesr desirable that an aircraftbe able to fly from a given station a particular dis-tance. therefroml in a given direction so that lloy merely reading the instruments the pilo-twill know exactly where he is. Such a result. can be accomplished loy'use of' a distance finding system in accordance with my invention in conjunction with a direction finder of Figs. 6 and 7, and. a gym-compass. However, it is-desirable to have as little `apparatus-on the craft as possible. This may be accomplished by using on the ground?, equipment to produce direction guiding insteadof using a= direction finder on the craft.

In Fig. 8 an embodiment of myf invention whereby the pilot may be enabledV to ascertain his position from a given retransmi-ttingv station is illustrated. In this arrangement at the transmitting station 8U, is provided a repeaterstation of the type above described', whereby thev pilot of the craft 8i may ascertain his distance fromthe transmitting station. Also, at station is provided a beaconV transmitter ofv any known type which defines a given' course-'- line. `The pilot remains sothat he then merely need follow the given course line until his indicator of distance Vd reads the desired value. c Then by use of a suitable altimeter, preferablya radioaltimeter, it is possible to fly at any desired height h, with respect to the ground surface at, the particular distance d. In order to obtain these indications it is necessary that the aircraft carry the ordinary beacon receiving arrangement andinaddition the distance finding system described in the present application and an accurate altimeter to indicate his altitude with respect to the earth. Since the altimeter and beacon receiver are generally standard equipment only the distance finder represents added apparatus. With this arrangement it is possible for apilot of a craft to ascertain his positionr withoutbeing able to sight the ground. While the height must be taken into consideration for precise calculation of the distance along the ground, in practice this generally is not necessary since the angle included between ground and the line d is so small that this indicated distance is substantially equal tothe groundl distance. A

With these systems it is often desirable that the'v radiations from the beacon be such that it isnotdetectable at the ground level. Accordingly, an arrangement as disclosed in Fig. 9 may be used rather than the beacon system producing the field pattern of Fig. 8. In accordance with this arrangement of Fig. 9 the transmitter station may transmit abeacon guiding system at an angle to the earth, so that substantially no radiation occurs along the earths surface itselfj.` Ii'l the beacon isdesiened so as to produce only a single guide line, for example, by utilizing fourintersecting patterns instead of two to define the beacon range, then thecraft 8l need not carry an Valtimeter but need merely follow this single line until the meter on the plane indicates thaty the proper distance has been reached. 'I-he antenna of the repeater station should also be of such construction that radiationtherefrom is directed away from the earth. This may be accomplished by the use of properly designed radiators or vby various refiectorl arrangements as known in the art. Since the radiation as exemplied by the conical patterns say 83, is not perceptible at the surface of the earth at the position P, it is not possible for those at this position to know that the beacon is pointed in their 50 direction.

If the beacon pattern 83 is not suiciently narrow or if a single guide line is not provided, craft 8l may carry an altimeter for use in connection with the distance finder and beacon for precisely determining its position.

While I have described a few embodiments of my invention in connection with the accompanying drawings, it should be clearly understood that these are made merely by way of illustration. It is clear that each of the various embodiments illustrated in the figures may be modified by transposing and combining various elements of the systems illustrated as desired. Furthermore,

'any known type of recording arrangement and reproducing arrangement may be used instead of the photoelectric control arrangement disclosed in connection with Fig. 5. Likewise, it should -be understood that at the receiving station, Figs. 6 and '7, various known arrangements for preventing coupling between antennae such as 'I2 and 'I3 may be provided. These may constitute, for example, shield arrangements to prevent any coupling. Other known arrangements such as systems for feeding over a portion of the 65 sponsive to receipt of said energy in opposite phase so as to overcomewthe 10 to secure protection is embodied in the accompanying claims.

What I claim is:

A1. Adistance determining system, comprising means for transmitting radio frequency waves of cyclically varying frequency from a first station, means at a second station comprising a repeater for receiving said radio frequency waves and transmitting therefrom under control of said received waves corresponding radio frequency waves cyclically varying in frequency,

means at said first station for receiving the Waves transmitted from said second station and other waves varying in frequency corresponding to the frequency variations of waves from said first named transmitting means, and means at said first` station responsive to said received Waves and said other waves for comparing the frequency of said received waves and said energy for determining the distance between said first and second stations.

2. A distance determining system according to claim 1, further comprising direction finder means at said first station to indicate direction toward lsaid second station, whereby the position of said first station with respect tosaid second station may be determined. Y,

3. VA distance determining system according to claim l, further comprising means for intermittently interrupting transmission of said frequency variablewaves at said second station, and

means-for transmitting other signals therefrom during saidperiod of interruption.

4. A'distance determining system according to claim 1, further comprising energy supply means at saidsecond station and means at said second station responsive to energy received from said first station for supplying energizing power to said radio transmitting means at said second station from said energy supply means.

5. A distance determining system according to claim 1, wherein said waves transmitted from said second station are of the same frequency range as the vwaves received thereat from said first station, further .comprising `circuit means for preventing waves transmitted from said second station from affecting the operation of the receiving means at said second station.l

6. In an aircraft positionl determining system, a transmitting station, means at said station for defining a radio beacon guiding course, means for determining the distance of said craft from said transmitting station comprising-,a cyclically variable frequency transmitter carried bysaid aircraft, means at said transmitting station revariable frequency waves for retransmitting to said craftr waves correspondingly variable in frequency, and means on said aircraft for receiving said retransmitted Waves and comparing them with said transmitted waves to determine distance, and means on said aircraft responsive to received energy for indicating when said Vaircraft 'is following said beacon guide course.

7. A navigation system for aircraft` comprising means for transmitting radio frequency Waves of cyclically varying frequency from a first station, means at a second station comprising a repeater for receiving said radio frequency Waves and transmitting therefrom under control of said received waves radio frequency waves correspondingly cyclically varying in frequency, means at said first station for receiving the Waves transmitted from said second station and for receiving other waves Within the range of frequencies over which said first-mentioned transmitted waves are varied and means at said first station for comparing the frequencies of said received waves with the instantaneous frequency of said first-mentioned transmitted Waves.

8. A navigation system for aircraft comprising means for transmitting radio frequency Waves of cyclically varying frequency from a first station, a second station comprising a repeater for receiving said transmitted waves and for retransmitting said Waves, means at said first station for receiving the Waves transmitted from said second station and for receiving other waves within the range of frequencies over which said first-mentioned transmitted waves are varied, and means at said rst station for comparing the frequencies of said received waves with the instantaneous frequency of said first-mentioned transmitted Waves.

9. A navigation system for aircraft comprising means for transmitting radio frequency Waves of cyclically varying frequency from a rst station, a second station comprising a repeater for receiving said transmitted Waves and for retransmitting said Waves, means at said first station for receiving the waves transmitted from said second station and for receiving other Waves Within the range of frequencies over which said first-mentioned transmitted waves are Varied, said other Waves including waves transmitted from said rst station and reflected by objects external to said first station, and means at said rst station for comparing the frequencies of said received Waves With the instantaneous frequency of said first-mentioned transmitted waves.

WILLIAM H. CAPEN. 

